Senior White House aide Karl Rove has announced that he is resigning from the White House at the end of August.
Mr Rove, who has advised George Bush since the United States president announced he was running for governor of Texas, said he wanted to spend more time with his family.
He is expected to return to Texas, where his family resides, after securing two terms for Mr Bush since he began advising him.
Mr Rove was known as the Republicans' election specialist, fending off two separate Democratic challengers.
In an interview with the Wall Street Journal he said: "I just think it's time. There's always something that can keep you here and as much as I'd like to be here, I've got to do this for the sake of my family."
White House chief of staff Josh Bolten had said that any members of the administration who stayed beyond Labor Day in the US would have to see out Mr Bush's full second term till January 2009.
Mr Rove told the US paper that he believed the Democrats would elect for Hillary Clinton as the party's presidential candidate, who he described as a "fatally flawed" nominee.
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